scholarly journals The GAPS Programme at TNG

2020 ◽  
Vol 642 ◽  
pp. A133 ◽  
Author(s):  
M. Damasso ◽  
A. F. Lanza ◽  
S. Benatti ◽  
V. M. Rajpaul ◽  
M. Mallonn ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Magnetic Activity ◽  
Young Stars ◽  
Radial Velocities ◽  
Occurrence Rate ◽  
Formation Mechanisms ◽  
And Migration ◽  
Velocity Scatter ◽  
Key Aspects ◽  
Migration Pathways

Context. Detecting and characterising exoworlds around very young stars (age ≤10 Myr) are key aspects of exoplanet demographic studies, especially for understanding the mechanisms and timescales of planet formation and migration. Any reliable theory for such physical phenomena requires a robust observational database to be tested. However, detection using the radial velocity method alone can be very challenging because the amplitude of the signals caused by the magnetic activity of such stars can be orders of magnitude larger than those induced even by massive planets. Aims. We observed the very young (~2 Myr) and very active star V830 Tau with the HARPS-N spectrograph between October 2017 and March 2020 to independently confirm and characterise the previously reported hot Jupiter V830 Tau b (Kb = 68 ± 11 m s−1; mb sin ib = 0.57 ± 0.10 MJup; Pb = 4.927 ± 0.008 d). Methods. Because of the observed ~1 km s−1 radial velocity scatter that can clearly be attributed to the magnetic activity of V830 Tau, we analysed radial velocities extracted with different pipelines and modelled them using several state-of-the-art tools. We devised injection-recovery simulations to support our results and characterise our detection limits. The analysis of the radial velocities was aided by a characterisation of the stellar activity using simultaneous photometric and spectroscopic diagnostics. Results. Despite the high quality of our HARPS-N data and the diversity of tests we performed, we were unable to detect the planet V830 Tau b in our data and cannot confirm its existence. Our simulations show that a statistically significant detection of the claimed planetary Doppler signal is very challenging. Conclusions. It is important to continue Doppler searches for planets around young stars, but utmost care must be taken in the attempt to overcome the technical difficulties to be faced in order to achieve their detection and characterisation. This point must be kept in mind when assessing their occurrence rate, formation mechanisms, and migration pathways, especially without evidence of their existence from photometric transits.

scholarly journals A HARPS RV search for planets around young nearby stars

2020 ◽  
Vol 633 ◽  
pp. A44 ◽  
Author(s):  
A. Grandjean ◽  
A.-M. Lagrange ◽  
M. Keppler ◽  
N. Meunier ◽  
L. Mignon ◽  
...  
Keyword(s):  
Time Series ◽  
Radial Velocity ◽  
Spectroscopic Data ◽  
Imaging Techniques ◽  
Giant Planet ◽  
Magnetic Activity ◽  
Young Stars ◽  
Upper Limits ◽  
Nearby Stars ◽  
Low Mass

Context. Young nearby stars are good candidates in the search for planets with both radial velocity (RV) and direct imaging techniques. This, in turn, allows for the computation of the giant planet occurrence rates at all separations. The RV search around young stars is a challenge as they are generally faster rotators than older stars of similar spectral types and they exhibit signatures of magnetic activity (spots) or pulsation in their RV time series. Specific analyses are necessary to characterize, and possibly correct for, this activity. Aims. Our aim is to search for planets around young nearby stars and to estimate the giant planet (GP) occurrence rates for periods up to 1000 days. Methods. We used the HARPS spectrograph on the 3.6 m telescope at La Silla Observatory to observe 89 A−M young (<600 Myr) stars. We used our SAFIR (Spectroscopic data via Analysis of the Fourier Interspectrum Radial velocities) software to compute the RV and other spectroscopic observables. Then, we computed the companion occurrence rates on this sample. Results. We confirm the binary nature of HD 177171, HD 181321 and HD 186704. We report the detection of a close low mass stellar companion for HIP 36985. No planetary companion was detected. We obtain upper limits on the GP (<13 MJup) and BD (∈ [13;80] MJup) occurrence rates based on 83 young stars for periods less than 1000 days, which are set, 2−2+3 and 1−1+3%.

scholarly journals Spin-orbit alignment and magnetic activity in the young planetary system AU Mic

2020 ◽  
Vol 641 ◽  
pp. L1 ◽  
Author(s):  
E. Martioli ◽  
G. Hébrard ◽  
C. Moutou ◽  
J.-F. Donati ◽  
É. Artigau ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Template Matching ◽  
Near Infrared ◽  
Rotation Axis ◽  
Magnetic Activity ◽  
Radial Velocities ◽  
Model Parameters ◽  
Correlation Technique ◽  
Spin Orbit ◽  
Stellar Rotation

We present high-resolution near-infrared spectropolarimetric observations using the SPIRou instrument at Canada-France-Hawaii Telescope (CFHT) during a transit of the recently detected young planet AU Mic b, with supporting spectroscopic data from iSHELL at NASA InfraRed Telescope Facility. We detect Zeeman signatures in the Stokes V profiles and measure a mean longitudinal magnetic field of ¯Bℓ = 46.3 ± 0.7 G. Rotationally modulated magnetic spots likely cause long-term variations of the field with a slope of dBℓ/dt = −108.7 ± 7.7 G d−1. We apply the cross-correlation technique to measure line profiles and obtain radial velocities through CCF template matching. We find an empirical linear relationship between radial velocity and Bℓ, which allows us to estimate the radial-velocity induced by stellar activity through rotational modulation of spots for the five hours of continuous monitoring of AU Mic with SPIRou. We model the corrected radial velocities for the classical Rossiter-McLaughlin effect, using MCMC to sample the posterior distribution of the model parameters. This analysis shows that the orbit of AU Mic b is prograde and aligned with the stellar rotation axis with a sky-projected spin-orbit obliquity of λ = 0°−15°+18°. The aligned orbit of AU Mic b indicates that it formed in the protoplanetary disk that evolved into the current debris disk around AU Mic.

scholarly journals ESPRESSO highlights the binary nature of the ultra-metal-poor giant HE 0107−5240

2020 ◽  
Vol 633 ◽  
pp. A129
Author(s):  
P. Bonifacio ◽  
P. Molaro ◽  
V. Adibekyan ◽  
D. Aguado ◽  
Y. Alibert ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Radial Velocity ◽  
Binary Systems ◽  
Radial Velocities ◽  
Formation Mechanisms ◽  
Synthetic Spectrum ◽  
Low Carbon ◽  
Long Period ◽  
Low Metallicity ◽  
Velocity Variations

Context. The vast majority of the known stars of ultra low metallicity ([Fe/H] <  −4.5) are known to be enhanced in carbon, and belong to the “low-carbon band” (A(C) = log(C/H)+12 ≤ 7.6). It is generally, although not universally, accepted that this peculiar chemical composition reflects the chemical composition of the gas cloud out of which these stars were formed. The first ultra-metal-poor star discovered, HE 0107−5240, is also enhanced in carbon and belongs to the “low-carbon band”. It has recently been claimed to be a long-period binary, based on radial velocity measurements. It has also been claimed that this binarity may explain its peculiar composition as being due to mass transfer from a former AGB companion. Theoretically, low-mass ratios in binary systems are much more favoured amongst Pop III stars than they are amongst solar-metallicity stars. Any constraint on the mass ratio of a system of such low metallicity would shed light on the star formation mechanisms in this metallicity regime. Aims. We acquired one high precision spectrum with ESPRESSO in order to check the reality of the radial velocity variations. In addition we analysed all the spectra of this star in the ESO archive obtained with UVES to have a set of homogenously measured radial velocities. Methods. The radial velocities were measured using cross correlation against a synthetic spectrum template. Due to the weakness of metallic lines in this star, the signal comes only from the CH molecular lines of the G-band. Results. The measurement obtained in 2018 from an ESPRESSO spectrum demonstrates unambiguously that the radial velocity of HE 0107−5240 has increased from 2001 to 2018. Closer inspection of the measurements based on UVES spectra in the interval 2001–2006 show that there is a 96% probability that the radial velocity correlates with time, hence the radial velocity variations can already be suspected from the UVES spectra alone. Conclusions. We confirm the earlier claims of radial velocity variations in HE 0107−5240. The simplest explanation of such variations is that the star is indeed in a binary system with a long period. The nature of the companion is unconstrained and we consider it is equally probable that it is an unevolved companion or a white dwarf. Continued monitoring of the radial velocities of this star is strongly encouraged.

scholarly journals The TROY project: Searching for co-orbital bodies to known planets

2018 ◽  
Vol 609 ◽  
pp. A96 ◽  
Author(s):  
J. Lillo-Box ◽  
D. Barrado ◽  
P. Figueira ◽  
A. Leleu ◽  
N. C. Santos ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Planetary Systems ◽  
Occurrence Rate ◽  
Velocity Data ◽  
Transiting Planets ◽  
Extrasolar Systems ◽  
Upper Limits ◽  
And Migration ◽  
The Masses ◽  
Radial Velocity Data

Context. The detection of Earth-like planets, exocomets or Kuiper belts show that the different components found in the solar system should also be present in other planetary systems. Trojans are one of these components and can be considered fossils of the first stages in the life of planetary systems. Their detection in extrasolar systems would open a new scientific window to investigate formation and migration processes. Aims. In this context, the main goal of the TROY project is to detect exotrojans for the first time and to measure their occurrence rate (η-Trojan). In this first paper, we describe the goals and methodology of the project. Additionally, we used archival radial velocity data of 46 planetary systems to place upper limits on the mass of possible trojans and investigate the presence of co-orbital planets down to several tens of Earth masses. Methods. We used archival radial velocity data of 46 close-in (P < 5 days) transiting planets (without detected companions) with information from high-precision radial velocity instruments. We took advantage of the time of mid-transit and secondary eclipses (when available) to constrain the possible presence of additional objects co-orbiting the star along with the planet. This, together with a good phase coverage, breaks the degeneracy between a trojan planet signature and signals coming from additional planets or underestimated eccentricity. Results. We identify nine systems for which the archival data provide >1σ evidence for a mass imbalance between L4 and L5. Two of these systems provide >2σ detection, but no significant detection is found among our sample. We also report upper limits to the masses at L4/L5 in all studied systems and discuss the results in the context of previous findings.

scholarly journals So close, so different: characterization of the K2-36 planetary system with HARPS-N

2019 ◽  
Vol 624 ◽  
pp. A38 ◽  
Author(s):  
M. Damasso ◽  
L. Zeng ◽  
L. Malavolta ◽  
A. Mayo ◽  
A. Sozzetti ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Gaussian Process Regression ◽  
Magnetic Activity ◽  
Good Precision ◽  
Stellar Activity ◽  
Transiting Planets ◽  
Atmospheric Escape ◽  
Low Mass ◽  
Time Variations ◽  
Velocity Scatter

Context. K2-36 is a K dwarf orbited by two small (Rb = 1.43 ± 0.08 R⊕ and Rc = 3.2 ± 0.3 R⊕), close-in (ab = 0.022 au and ac = 0.054 au) transiting planets discovered by the Kepler/K2 space observatory. They are representatives of two distinct families of small planets (Rp < 4 R⊕) recently emerged from the analysis of Kepler data, with likely a different structure, composition and evolutionary pathways. Aims. We revise the fundamental stellar parameters and the sizes of the planets, and provide the first measurement of their masses and bulk densities, which we use to infer their structure and composition. Methods. We observed K2-36 with the HARPS-N spectrograph over ~3.5 yr, collecting 81 useful radial velocity measurements. The star is active, with evidence for increasing levels of magnetic activity during the observing time span. The radial velocity scatter is ~17 m s−1 due to the stellar activity contribution, which is much larger that the semi-amplitudes of the planetary signals. We tested different methods for mitigating the stellar activity contribution to the radial velocity time variations and measuring the planet masses with good precision. Results. We find that K2-36 is likely a ~1 Gyr old system, and by treating the stellar activity through a Gaussian process regression, we measured the planet masses mb = 3.9 ± 1.1 M⊕ and mc = 7.8 ± 2.3 M⊕. The derived planet bulk densities ρb = 7.2−2.1+2.5 g cm−3 and ρc = 1.3−0.5+0.7 g cm−3 point out that K2-36 b has a rocky, Earth-like composition, and K2-36 c is a low-density sub-Neptune. Conclusions. Composed of two planets with similar orbital separations but different densities, K2-36 represents an optimal laboratory for testing the role of the atmospheric escape in driving the evolution of close-in, low-mass planets after ~1 Gyr from their formation. Due to their similarities, we performed a preliminary comparative analysis between the systems K2-36 and Kepler-36, which we deem worthy of a more detailed investigation.

scholarly journals Search for associations containing young stars (SACY)

2020 ◽  
Vol 645 ◽  
pp. A30
Author(s):  
S. Zúñiga-Fernández ◽  
A. Bayo ◽  
P. Elliott ◽  
C. Zamora ◽  
G. Corvalán ◽  
...  
Keyword(s):  
High Resolution ◽  
Radial Velocity ◽  
Cross Correlation ◽  
Young Stars ◽  
Radial Velocities ◽  
Spectroscopic Binaries ◽  
Substellar Objects ◽  
Apparent Variation ◽  
Stellar Associations

Context. Nearby young associations offer one of the best opportunities for a detailed study of the properties of young stellar and substellar objects thanks to their proximity (<200 pc) and age (∼5−150 Myr). Previous works have identified spectroscopic (<5 au) binaries, close (5−1000 au) visual binaries, and wide or extremely wide (1000−100 000 au) binaries in the young associations. In most of the previous analyses, single-lined spectroscopic binaries (SB1) were identified based on radial velocities variations. However, this apparent variation may also be caused by mechanisms unrelated to multiplicity. Aims. We seek to update the spectroscopy binary fraction of the Search for Associations Containing Young stars (SACY) sample, taking into consideration all possible biases in our identification of binary candidates, such as activity and rotation. Methods. Using high-resolution spectroscopic observations, we produced ∼1300 cross-correlation functions (CCFs) to disentangle the previously mentioned sources of contamination. The radial velocity values we obtained were cross-matched with the literature and then used to revise and update the spectroscopic binary (SB) fraction in each object of the SACY association. In order to better describe the CCF profile, we calculated a set of high-order cross-correlation features to determine the origin of the variations in radial velocities. Results. We identified 68 SB candidates from our sample of 410 objects. Our results hint that at the possibility that the youngest associations have a higher SB fraction. Specifically, we found sensitivity-corrected SB fractions of 22−11+15% for ϵ Cha, 31−14+16% for TW Hya and 32−8+9% for β Pictoris, in contrast to the five oldest associations we have sampled (∼35−125 Myr) which are ∼10% or lower. This result seems independent of the methodology used to asses membership to the associations. Conclusions. The new CCF analysis, radial velocity estimates, and SB candidates are particularly relevant for membership revision of targets in young stellar associations. These targets would be ideal candidates for follow-up campaigns using high-resolution techniques to confirm binarity, resolve orbits, and, ideally, calculate dynamical masses. Additionally, if the results on the SB fraction in the youngest associations were confirmed, it could hint at a non-universal multiplicity among SACY associations.

scholarly journals Anatomy of a Misfit: International Migration Statistics

2021 ◽  
Vol 13 (7) ◽  
pp. 4032
Author(s):  
Ahmad Wali Ahmad-Yar ◽  
Tuba Bircan
Keyword(s):  
United Nations ◽  
International Migration ◽  
Time Lag ◽  
Data Systems ◽  
The Sustainable Development ◽  
High Commissioner ◽  
And Migration ◽  
Ultimate Objective ◽  
Nations Department ◽  
Key Aspects

Migration is one of the key aspects of the Sustainable Development Goals (SDGs). To understand global migration patterns, develop scenarios, design effective policies, focus on the population’s needs, and identify how these needs change over time, we need accurate, reliable and timely data. The gaps in international migration data have persisted since international organizations collect data. To improve the data gaps, there is a need to conceptualize the types of gaps and pinpoint the gaps within the international data systems. To that end, the ultimate objective of this paper is twofold, (i) to review and categorize the gaps in the literature and (ii) assess the statistical data sources, i.e., United Nations Department of Social and Economic Affairs (UN DESA), Organization for Economic Co-operation and Development (OECD), International Organization for Migration (IOM), Eurostat, and the United Nations High Commissioner for Refugees (UNHCR). Our results demonstrate that the gaps could be categorized under (1) definitions and measures, (2) drivers or reasons behind migration, (3) geographic coverage, (4) gaps in demographic characteristics and (5) the time lag in the availability of data. The reviewed sources suffer from the gaps, which are not mutually exclusive (they are interlinked): the quality and availability of both migration flows and stocks data vary across regions and countries, and migration statistics highly rely on immigrants’ arrival.

scholarly journals Invasive Plant Species Distribution Is Structured by Soil and Habitat Type in the City Landscape

Plants ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 773
Author(s):  
Ilona Szumańska ◽  
Sandra Lubińska-Mielińska ◽  
Dariusz Kamiński ◽  
Lucjan Rutkowski ◽  
Andrzej Nienartowicz ◽  
...  
Keyword(s):  
Distribution Pattern ◽  
Species Distribution ◽  
Human Activities ◽  
Invasive Plant ◽  
Habitat Type ◽  
Permanent Plots ◽  
Human Land Use ◽  
And Migration ◽  
Migration Pathways ◽  
The City

Invasive alien species (IAS) is a global problem that largely relates to human activities and human settlements. To prevent the further spread of IAS, we first need to know their pattern of distribution, to determine which constitutes the greatest threat, and understand which habitats and migration pathways they prefer. Our research aimed to identify the main vectors and distribution pattern of IAS of plants in the city environment. We checked the relations between species distribution and such environmental factors as urban soil type and habitat type. We applied data on IAS occurrence (collected in the period 1973–2015) in 515 permanent plots with dimensions of 0.5 × 0.5 km and analyzed by direct ordination methods. In total, we recorded 66 IAS. We found a 27% variance in the IAS distribution pattern, which can be explained by statistically significant soil and habitat types. The most important for species distribution were: river and alluvial soils, forests and related rusty soils, and places of intensive human activities, including areas of urbisols and industriosols. Our results provide details that can inform local efforts for the management and control of invasive species, and they provide evidence of the different associations between natural patterns and human land use.

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